1. Field of the Invention
The present invention relates to an electroconductive material and a method of producing thereof.
2. Description of the Related Art
In recent years, an image display device (display) represented by a liquid crystal display (LCD), a plasma display panel (PDP), an electroluminescence (EL) element and the like have become used widely in various fields such as television sets, computers, various kinds of mobile devices and others that have recently become popular. On the other hand, a solar cell has been focused as an energy source replaceable for fossil energy, and a solar cell with high-performance or the like has been requested to be developed in order to meet further popularization thereof. In these display devices and solar cells, an electroconductive film is used.
Generally, electroconductive films using a metallic material, such as ITO-based electroconductive films, are produced by forming, on a glass substrate, a film from a metallic material by a vapor phase method such as a vacuum deposition method or a sputtering method. Display devices such as portable telephones and mobile instruments have been becoming lighter in weight, and it has been demanded that a display device substrate be shifted from glass to plastic. The introduction of a plastic substrate has reduced the weight of display devices to become half or less in comparison to the convectional products, and a plastic substrate has been remarkably improved in strength and impact resistance.
There, however, is a problem with regard to ITO-based electroconductive films in that the substitution of glass substrates with plastic films results in a decrease in adhesiveness, and making a substrate and a formed electroconductive film prone to easily peel apart from each other. Moreover, metallic materials, such as ITO, are ordinarily formed into a film by using a vapor phase method such as sputtering, so that an expensive production apparatus needs to be used.
As an electroconductive material replaceable for these, a coating type electroconductive material including a π-electron conjugated polymer that is an electroconductive polymer, a silver nano-wire, and a carbon material such as a carbon nano-tube or a grapheme is known. The use of an electroconductive polymer allows a conductive thin film to be formed by coating and offers the advantage that a conductive thin film may be inexpensively produced. Moreover, an electrode made of an electroconductive polymer is more flexible and less brittle than ITO electrodes, and it therefore is less prone to break even though it is used for flexible items. Accordingly, it is advantageous to apply an electrode made of an electroconductive polymer to touch panels that specifically require high flexibility, since lifetime may be extended in view of durability and reliability of apparatuses.
As such an electroconductive polymer, polythiophene containing polyanion has been developed, and a technique for forming an electroconductive film by using this polymer is disclosed in the specification of European Patent No. 440957. It, however, has become clear that this electroconductive film is slightly weaker in durability than ITO films and the like and that it may not achieve a durability sufficient for practical use in some applications. In particular, when the electroconductive films are used for a display device, durability against light is important, that is, transparency or electrical conductivity is required not to be lowered even after the films are irradiated with light of a certain level or more. In addition to that, the electrical conductivity has been found to be also lowered by an action of humidity or heat.
Further, these electroconductive films are poor in adhesion in some cases and have been found not to have practically sufficient adhesion in a certain application. Therefore, an attempt of improving the adhesion by using the electroconductive films in combination with an adhesive layer is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 2007-510807.
However, also in this case, practically sufficient adhesion and durability have been found not to be attained in a certain application.